Inspection method and inspection apparatus

ABSTRACT

A workpiece having an outer peripheral portion rotationally symmetric about a symmetry axis can be inspected with high-accuracy while reducing cycle time of the inspection. In an inspection for each of the workpieces, on the basis of the image of the workpiece acquired by executing a first step of capturing an image of the workpiece while holding the workpiece at a pre-alignment position using a holding table and rotating the workpiece about a rotary axis, a position of the workpiece at the holding table is corrected so as to eliminate misalignment of the symmetry axis with respect to the rotary axis. Thereafter, on the basis of the image acquired by executing a fifth step of capturing an image of the workpiece while rotating the workpiece about the rotary axis at an inspection position, the workpiece is inspected. In the inspection of the workpiece, the fifth step for a previous workpiece of two consecutive workpieces and the first step for a next workpiece are executed in parallel with each other.

CROSS REFERENCE

This application is the U.S. National Phase under 35 U.S.C. § 371 ofinternational Application No. PCT/JP2017/040422, filed on Nov. 9, 2017,which claims the benefit of Japanese Application No. 2017-047287, filedon Mar. 13, 2017, the entire contents of each are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to an inspection method and an inspectionapparatus for inspecting a workpiece having an outer peripheral portionrotationally symmetric about a symmetry axis.

BACKGROUND ART

A workpiece inspection apparatus described in patent literature 1 isknown as an example of an apparatus for inspection of the appearance ofa workpiece rotationally symmetric about a symmetry axis. In theworkpiece inspection apparatus, the workpiece is held by a holder unitconnected to a motor. While the workpiece is rotated by the motor,multiple cameras capture images of the workpiece and the appearance ofthe workpiece are inspected on the basis of the captured images.

CITATION LIST Patent Literature

[Patent Literature 1] JP 2012-63268 A

SUMMARY OF INVENTION Technical Problem

The apparatus described in patent literature 1 inspects a gear as aworkpiece for any scratches, defects, etc. In the apparatus, the holderunit includes a shaft passed through a through hole penetrating theworkpiece in an axis direction, and a clamp mechanism that clamps theworkpiece coaxially with the shaft. In response to the rotation of arotary axis of the motor, the shaft and the workpiece rotate integrally.If the symmetry axis of the workpiece is not matched with the rotaryaxis of the motor, namely, on the occurrence of misalignment, it becomesdifficult to conduct high-accuracy inspection on the basis of thecaptured images. This type of workpiece is produced in large quantities.To respond to such production, it is necessary to inspect the workpiecesone by one in succession. This necessitates not only accuracy but alsoreduction in what is called cycle time meaning a length of time requiredfor inspection of one workpiece.

The present invention has been made in view of the foregoing problems,and is intended to provide an inspection method and an inspectionapparatus allowing high-accuracy inspection of a workpiece having anouter peripheral portion rotationally symmetric about a symmetry axisand reduction in cycle time of the inspection.

Solution to Problem

One aspect of the invention is an inspection method of inspecting aplurality of workpieces one by one in succession, each of the workpieceshaving an outer peripheral portion rotationally symmetric about asymmetry axis, characterized in that an inspection for each of theworkpieces is performed by executing: a first step of capturing an imageof the workpiece while holding the workpiece at a pre-alignment positionusing a holding table and rotating the workpiece about a rotary axis; asecond step of moving the holding table holding the workpiece to aninspection position different from the pre-alignment position after thefirst step; a third step of detecting misalignment of the symmetry axisof the workpiece with respect to the rotary axis on the basis of theimage of the workpiece captured in the first step; a fourth step ofcorrecting a position of the workpiece at the holding table so as toeliminate the misalignment detected in the third step; a fifth step ofcapturing an image of the workpiece that have undergone a positioncorrection while rotating the workpiece about the rotary axis at theinspection position; and a sixth step of inspecting the workpiece on thebasis of the image captured in the fifth step, and the fifth step for aprevious workpiece of two consecutive workpieces and the first step fora next workpiece are executed in parallel with each other.

Other aspect of the invention is an inspection apparatus comprising: aholding table that holds a workpiece having an outer peripheral portionrotationally symmetric about a symmetry axis and rotates the workpieceabout a rotary axis; an alignment imaging part that captures an image ofthe workpiece held by the holding table at a pre-alignment position; aninspection imaging part that captures an image of the workpiece held bythe holding table at an inspection position different from thepre-alignment position; a workpiece position correction part thatcorrects the position of the workpiece, having misalignment of thesymmetry axis with respect to the rotary axis, on the basis of an imageacquired by imaging of the workpiece using the alignment imaging partwhile the workpiece is rotated about the rotary axis; and a workpieceinspection part that inspects the workpiece that have undergone aposition correction on the basis of an image acquired by imaging of theworkpiece using the inspection imaging part while the workpiece isrotated about the rotary axis, wherein the holding table includes aplurality of holding tables, and one of the holding tables is located atthe pre-alignment position while one of the remaining holding tables islocated at the inspection position, whereby imaging of the workpiecehaving the misalignment by the alignment imaging part and imaging of theworkpiece having undergone the position correction by the inspectionimaging part are executed in parallel with each other.

According to the invention having the foregoing configuration, beforethe inspection imaging part captures an image of each workpiece and thenthe workpiece is inspected, the workpiece position is corrected at theholding table. More specifically, on the basis of an image of theworkpiece acquired by imaging of the workpiece while the workpiece heldby the holding table is rotated about the rotary axis, the workpieceposition is corrected at the holding table so as to eliminatedisplacement of the symmetry axis with respect to the rotary axis,namely, misalignment. Thus, influence of the misalignment is absent inan image acquired by imaging of the workpiece held by the holding tableusing the inspection imaging part while the workpiece is rotated aboutthe rotary axis, so that inspection can be conducted with high accuracyon the basis of the acquired image.

As described above, the workpiece position correction before inspection,so-called pre-alignment process is a factor of deterioration of cycletime. However, according to the present invention, imaging of the nextworkpiece by the alignment imaging part proceeds in parallel withimaging of the previous workpiece for inspection by the inspectionimaging part during inspection of the workpiece one by one continuously.In this way, parts of respective processes for two consecutiveworkpieces are executed in parallel with each other to achieve reductionin cycle time. Note that in the present invention, “in parallel” meansthat some or all of imaging of the previous workpiece temporallyoverlaps some or all of imaging of the next workpiece.

Advantageous Effects of Invention

As described above, according to the present invention, the misalignmentis eliminated before the workpiece is inspected to allow high-accuracyinspection of the workpiece. Further, the cycle time can be shortenedbecause the imaging of the next workpiece for detecting the misalignmentis executed in parallel with the imaging of the previous workpiece forinspection.

All of a plurality of constituent elements of each aspect of theinvention described above are not essential and some of the plurality ofconstituent elements can be appropriately changed, deleted, replaced byother new constituent elements or have limited contents partiallydeleted in order to solve some or all of the aforementioned problems orto achieve some or all of effects described in this specification.Further, some or all of technical features included in one aspect of theinvention described above can be combined with some or all of technicalfeatures included in another aspect of the invention described above toobtain one independent form of the invention in order to solve some orall of the aforementioned problems or to achieve some or all of theeffects described in this specification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the entire configuration of one embodiment of an inspectionapparatus according to the present invention.

FIG. 2 is a block diagram showing the electrical configuration of theinspection apparatus shown in FIG. 1.

FIG. 3 is a perspective view showing the configuration of the workpieceholding unit.

FIG. 4 is a flowchart showing the operation of inspecting a workpiece bythe inspection apparatus in FIG. 1.

FIG. 5 schematically shows the inspecting operation.

FIG. 6 is a flowchart showing operation performed in inspecting multipleworkpieces continuously, one by one, using the inspection apparatus inFIG. 1.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows the entire configuration of one embodiment of an inspectionapparatus according to the present invention. FIG. 2 is a block diagramshowing the electrical configuration of the inspection apparatus shownin FIG. 1. The inspection apparatus 100 is to inspect the appearance ofa workpiece W such as a gear or an impeller having an outer peripheralportion of a rotationally symmetric shape about a symmetry axis withprojections and recesses provided periodically and repeatedly. Theinspection apparatus 100 includes a loading unit 1, a workpiece holdingunit 2, an imaging unit 3, an unloading unit 4, and a control unit 5. Asshown in FIG. 1, the workpiece W mentioned herein is a machine part witha shaft Wa and a gear Wb provided at the top of the shaft Wa and isformed by forging or casting, for example. After the part ismanufactured, the workpiece W is carried to the loading unit 1 by anexternal transfer robot or an operator.

The loading unit 1 includes a workpiece housing (not shown in thedrawings) such as a table or a storage locker. When a workpiece W istemporarily housed into the workpiece housing by the external transferrobot, for example, a workpiece detection sensor 11 (FIG. 2) at theworkpiece housing detects the workpiece W, and transmits a signalindicating the detection to the control unit 5 responsible for controlof the apparatus entirely. The loading unit 1 includes a loader 12 (FIG.2). In response to an operation command from the control unit 5, theloading unit 1 receives an uninspected workpiece W in the workpiecehousing and carries the uninspected workpiece W to the workpiece holdingunit 2.

FIG. 3 is a perspective view showing the configuration of the workpieceholding unit. The workpiece holding unit 2 is equipped with a holdingtable 21A and a holding table 21B for holding the workpiece W carried bythe loader 12. The holding tables 21A and 21B have the sameconfiguration and can hold the workpiece W by grasping a part of theshaft Wa of the workpiece W in a posture in which the gear Wb is in ahorizontal position. The configuration of the holding table 21A will bedescribed below by referring to FIG. 3. Meanwhile, as the holding table21B has the same configuration as the holding table 21A, the holdingtable 21B will be given the same signs as the holding table 21A and willnot be described.

As shown in FIG. 3, the holding table 21A includes a chuck mechanism 22,a horizontal positioning mechanism 23, a rotary mechanism 24, and avertical positioning mechanism 25 stacked in the vertical direction. Thechuck mechanism 22 includes movable members 221 to 223 substantiallyL-shaped in a side view, and a moving part 224 that moves the movablemembers 221 to 223 in conjunction with each other in a radial pattern inresponse to a movement command from the control unit 5. Each of themovable members 221 to 223 has an upper end surface where a projectionmember 225 is provided, and can be engaged with a stepped part of theshaft Wa using the upper end surface and the projection member 225.Thus, by moving the movable members 221 to 223 to get closer to eachother using the moving part 224 in response to a grasp command from thecontrol unit 5, it becomes possible to hold a workpiece W with thecenter axis of the chuck mechanism 22 (sign AX2 in FIG. 5) and the axisof the shaft Wa matched with each other. Meanwhile, by moving themovable members 221 to 223 to get away from each other using the movingpart 224 in response to a release command from the control unit 5, itbecomes possible to load an uninspected workpiece W using the loadingunit 1 or unload an inspected workpiece W using the unloading unit 4.

The chuck mechanism 22 having the foregoing configuration is supportedby the horizontal positioning mechanism 23. The horizontal positioningmechanism 23 includes what is called as an XY table for movements indirections orthogonal to each other in the horizontal direction. Thus,driving the XY table in response to a movement command from the controlunit 5 allows high-accuracy positioning of the chuck mechanism 22 on ahorizontal plane. Note that, as the XY table, a member using a motor anda ball screw mechanism in combination or a member using two linearmotors in combination orthogonal to each other in the horizontaldirection is applicable, for example.

The rotary mechanism 24 includes a motor 241. A rotary shaft (sign 242in FIG. 5) of the motor 241 extends vertically upwardly. The horizontalpositioning mechanism 23 is connected to the upper end of the rotaryshaft. Thus, when a rotation command is given from the control unit 5,the motor 241 is actuated to rotate the horizontal positioning mechanism23, the chuck mechanism 22, and a workpiece W grasped by the chuckmechanism 22 integrally about the rotary axis (sign AX3 in FIG. 5) ofthe motor 241.

In the embodiment, the horizontal positioning mechanism 23 is providedbetween the chuck mechanism 22 and the rotary mechanism 24, and this hasa technical significance of making the respective positions of the axisof the chuck mechanism 22, the symmetry axis (sign AX4 in FIG. 5) of thegear Wb of the workpiece W grasped by the chuck mechanism 22, and therotary axis of the motor 241 relative to each other adjustable using thehorizontal positioning mechanism 23. More specifically, matching thecenter axis of the chuck mechanism 22 and the rotary axis of the motor241 with each other allows the workpiece W grasped by the chuckmechanism 22 to rotate about the shaft Wa. In the presence ofdisplacement of the symmetry axis of the gear Wb from the shaft Wa,however, misalignment thereof with respect to the motor 241 occurs tocause unintentional eccentric rotation of the gear Wb. In response tothis, the horizontal positioning mechanism 23 is provided to achievedrive so as to correct the amount of the displacement and a direction ofthe displacement. By doing so, the symmetry axis of the gear Wb and therotary axis of the motor 241 can be matched with each other. This allowscapturing of an image of the gear Wb with high accuracy by the imagingunit 3. As a result, the workpiece W can be inspected with higheraccuracy.

The vertical positioning mechanism 25 includes a holding plate 251holding the motor 241, a base plate 252 arranged below the motor 241,four connecting pins 253 connecting the holding plate 251 and the baseplate 252, and an elevator 254 for moving the base plate 252 up and downin the vertical direction. The elevator 254 moves the base plate 252 upand down in response to an up-down command from the control unit 5 tomove the rotary mechanism 24, the horizontal positioning mechanism 23,and the chuck mechanism 22 integrally in the vertical direction. Bydoing so, a workpiece W can be located at an appropriate height positionat a pre-alignment position PA and an inspection position PI describednext.

As shown in FIG. 3, the holding tables 21A and 21B having the foregoingconfiguration are fixed on a support plate 261 while being separated bya certain distance. The support plate 261 is supported by a turningdriver 262 at an intermediate position between the holding tables 21Aand 21B. The turning driver 262 can make the support plate 261 turn 180degrees about a turning axis AX1 extending in the vertical direction inresponse to a turning command from the control unit 5. As shown in FIG.3, the turning driver 262 can make a switch between a first position atwhich the holding tables 21A and 21B are located at the pre-alignmentposition PA and the inspection position PI respectively, and a secondposition at which the holding tables 21A and 21B are located at theinspection position PI and the pre-alignment position PA respectively.For example, in parallel with pre-alignment process on a workpiece Wheld by the holding table 21A at the pre-alignment position PA, theturning driver 262 makes a switch from the first position to the secondposition to shift the holding table 21A from the pre-alignment positionPA to the inspection position PI. By doing so, the workpiece W afterbeing subjected to the pre-alignment process can be located at theinspection position PI. After inspection of this workpiece W isfinished, a turn is made in the opposite direction to shift the holdingtable 21A from the inspection position PI to the pre-alignment positionPA. By doing so, the workpiece W after being subjected to the inspectionprocess can be located at the pre-alignment position PA. In this way, inthe embodiment, the support plate 261 and the turning driver 262 form aposition switching mechanism 26 for switching the position of theworkpiece W.

As described above, the pre-alignment position PA is a position for thepre-alignment process. An alignment camera 27 is arranged above theholding table 21A (or 21B) located at the pre-alignment position PA. Asshown in FIG. 3, the alignment camera 27 is arranged on the oppositeside of the motor 241 with respect to a workpiece W, namely, above theworkpiece W. The alignment camera 27 includes a line sensor 271extending radially outwardly from the symmetry axis AX4 of the workpieceW. This allows imaging of the upper surface of the workpiece W by theline sensor 271 while rotating the workpiece W. By rotating theworkpiece W at least one turn, an image covering all the projections(teeth tips) and the recesses (teeth roots) at the outer peripheralportion of the gear Wb is acquired.

While not shown in FIG. 3, an alignment illuminator 28 (FIG. 2) isprovided that illuminates a workpiece W held by the holding table 21A(or 21B) for performing the alignment process favorably. Thus, duringcapturing of an image of the workpiece W by the alignment camera 27, theworkpiece W can be illuminated by the alignment illuminator 28 while theworkpiece W is rotated by the rotary mechanism 24. Data about the imageof the workpiece W is transmitted to the control unit 5 so that themisalignment is corrected to match the symmetry axis of the gear Wb andthe rotary axis of the motor 241 with each other, that is, apre-alignment process is performed.

The inspection position PI is a position at which the inspection processis performed. The imaging unit 3 is arranged above the holding table 21A(or 21B) located at the inspection position PI. At the inspectionposition PI, an image of a workpiece W can be captured by the imagingunit 3 while the workpiece W is rotated with the symmetry axis of thegear Wb and the rotary axis of the motor 241 matched with each other.Data about the image of the workpiece W is transmitted to the controlunit 5 to perform the inspection process of inspecting the workpiece Wfor the presence or absence of scratches, defects, etc. at the gear Wb.

As shown in FIG. 2, the imaging unit 3 includes multiple inspectioncameras 31 and multiple inspection illuminators 32. The inspectionilluminators 32 of the imaging unit 3 are arranged so as to illuminate aworkpiece W from various directions held by the holding table 21A (or21B) located at the inspection position PI. Images of the workpiece Wcan be captured from various directions by the inspection cameras 31while the workpiece W is rotated by the rotary mechanism 24 and theworkpiece W is illuminated by the inspection illuminators 32. Multiplepieces of data about the captured images are transmitted to the controlunit 5 and the workpiece W is inspected by the control unit 5.

The holding table 21A (or 21B) holding the inspected workpiece W isshifted from the inspection position PI to the pre-alignment position PAby the position switching mechanism 26 as described above. Then, theinspected workpiece W is carried out of the holding table 21A (or 21B)by the unloading unit 4. The unloading unit 4 is basically the same asthe loading unit 1. More specifically, the unloading unit 4 includes aworkpiece housing (not shown in the drawings) for temporarily housing aninspected workpiece W, a workpiece detection sensor 41 (FIG. 2), and anunloader 42 (FIG. 2). In response to an operation command from thecontrol unit 5, the unloading unit 4 carries the inspected workpiece Wfrom the holding table 21A (21B) to the workpiece housing.

As shown in FIG. 2, the control unit 5 is composed of a well-knowncentral processing unit (CPU) for implementation of logic operations, aread only memory (ROM) storing initial setting and others, a randomaccess memory (RAM) for temporarily storing various types of datagenerated during operation of the apparatus, etc. The control unit 5functionally includes an arithmetic processor 51, a memory 52, a drivecontroller 53, an external input and output part 54, an image processor55, and an illumination controller 56.

The drive controller 53 controls drive of driven mechanisms such as theloader 12 and the chuck mechanism 22 provided at corresponding positionsof the apparatus. The external input and output part 54 inputs signalsfrom various types of sensors installed on corresponding positions ofthe apparatus, and outputs signals to various types of actuators, etc.installed on corresponding positions of the apparatus. The imageprocessor 55 retrieves image data from the alignment camera 27 and theinspection camera 31 and performs image processing such as binarization.The illumination controller 56 controls turning-on, turning-off, etc. ofthe alignment illuminator 28 and the inspection illuminator 32.

The arithmetic processor 51 has an arithmetic function, and performs asequence of processes described next by controlling the drive controller53, the image processor 55, and the illumination controller 56 inaccordance with a program stored in the memory 52.

A sign 6 shown in FIG. 2 means a display unit functioning as aninterface with an operator. The display unit 6 is connected to thecontrol unit 5 to fulfill the function of displaying an operating stateof the inspection apparatus 100. Additionally, the display unit 6 isconfigured using a touch panel to fulfill a function as an inputterminal to accept input from an operator. The display unit 6 is notlimited to this configuration but can be configured using a displaydevice for display of an operating state and input terminals such as akeyboard and a mouse.

FIG. 4 is a flowchart showing the operation of inspecting a workpiece bythe inspection apparatus in FIG. 1. FIG. 5 schematically shows theinspecting operation. To clearly distinguish the operations of theholding tables 21A and 21B in FIG. 5, dots are given to the holdingtable 21B and a workpiece W held by the holding table 21B.

In the inspection apparatus 100, according to the inspection programstored in advance in the memory 52 of the control unit 5, the arithmeticprocessor 51 controls each part of the apparatus to execute thefollowing operations. Here, various operations performed on theworkpiece W will be described focusing on one workpiece W with referenceto FIGS. 4 and 5. When the control unit 5 confirms that there is noworkpiece W at the holding table 21A located at the pre-alignmentposition PA as shown in the section (a) of FIG. 5 and that the workpiecedetection sensor 11 detects an uninspected workpiece W housed in theworkpiece housing of the loading unit 1, the control unit 5 startsloading of the workpiece W onto the holding table 21A (step S1). In thisloading step, the loader 12 grasps the uninspected workpiece W locatedin the workpiece housing and carries the uninspected workpiece W fromthe loading unit 1 to the holding table 21A. In the embodiment, forsmoothly performing the loading step and a subsequent step of detectingmisalignment, before the workpiece W is carried to the holding table21A, the control unit 5 performs preparation for accepting the workpieceW in which the center axis AX2 of the chuck mechanism 22 and the rotaryaxis AX3 of the motor 241 are matched with each other by the horizontalpositioning mechanism 23 as shown in the section (a) of FIG. 5 and thethree movable members 221 to 223 are moved to get away from each other.

When the workpiece W is carried to the holding table 21A by the loader12, the chuck mechanism 22 moves the three movable members 221 to 223 toget closer to each other as described above to pinch a part of the shaftWa of the workpiece W and grasp the workpiece W. More specifically,during the loading operation, the movable members 221 to 223 are movedto get closer each other. While the respective upper end surfaces andthe respective projection members 225 of the movable members 221 to 223are engaged with the stepped part of the shaft Wa to match the centeraxis AX2 of the chuck mechanism 22 and the axis of the shaft Wa witheach other, the workpiece W is held (see the section (b) of FIG. 5). Inthis way, the loading step is finished. At the time of the finish, therotary axis AX3 of the motor 241, the center axis AX2 of the chuckmechanism 22, and the axis of the shaft Wa are matched with each other.However, in some case that the workpiece W is manufactured by forging orcasting, the symmetry axis AX4 of the gear Wb is displaced from the axisof the shaft Wa to cause misalignment of the workpiece W with respect tothe motor 241 as shown in the section (b) of FIG. 5, for example.

In this regard, in the embodiment, the uninspected workpiece W isilluminated by the alignment illuminator 28 (FIG. 2) and an image of thegear Wb is captured by the alignment camera 27 while the uninspectedworkpiece W is rotated by the motor 241 of the holding table 21A. Dataabout the image is stored into the memory 52 (step S2).

After this imaging is finished, the turning driver 262 makes a switchfrom the first position to the second position. More specifically, theturning driver 262 turns the support plate 261 180 degrees about theturning axis AX1. By doing so, as shown in the section (c) of FIG. 5,the holding table 21A holding the uninspected workpiece W is moved fromthe pre-alignment position PA to the inspection position PI and theelevator 254 moves the workpiece W to a height position at which animage of the workpiece W can be captured by the imaging unit 3 (stepS3).

In the embodiment, in parallel with the foregoing movements, the imagedata about the workpiece W is read from the memory 52 and misalignmentof the workpiece W with respect to the rotary mechanism 24 (motor 241)is detected (step S4). In the embodiment, the misalignment correspondsto information containing a displacement amount Δ and a displacementdirection. Next, the misalignment is corrected at the holding table 21A(step S5). This misalignment correction is made by moving the chuckmechanism 22 using the horizontal positioning mechanism 23 so as toeliminate the misalignment detected in step S4 described above. By doingso, as shown in the section (c) of FIG. 5, the symmetry axis of the gearWb and the rotary axis of the motor 241 are matched with each other atthe time of arrival of the holding table 21A at the inspection positionPI, or before or after the arrival. Thus, a workpiece imaging step (stepS6) can be started immediately.

In step S6, the rotary mechanism 24 of the holding table 21A located atthe inspection position PI is actuated to start workpiece rotation. Inthis step, the workpiece W held by the holding table 21A is in aso-called aligned state, which has undergone the foregoing misalignmentcorrection, and rotates about the symmetry axis AX4. In response to thisrotation, the plurality of inspection illuminators 32 are turned on toilluminate the rotating workpiece W from multiple directions. While theinspection illuminators 32 are turned on after the workpiece rotation,this is not the only timing for the turning-on. The turning-on of theinspection illuminators 32 may be started simultaneously with start ofthe rotation or before start of the rotation.

While the workpiece W is rotated and illuminated in this way, theplurality of inspection cameras 31 capture images of the workpiece Wfrom various directions, and image data about the images of theworkpiece W (hereinafter called “workpiece images”) captured from themultiple directions is transmitted to the control unit 5. The controlunit 5 stores the transmitted image data into the memory 52, andinspects the workpiece W on the basis of the stored image data byfollowing timing described below.

After the images are acquired in this way, the workpiece rotation isstopped at the holding table 21A, and the inspection illuminators 32 areturned off at the imaging unit 3. Further, the turning driver 262 turnsthe support plate 261 reversely 180 degrees about the turning axis AX1.By doing so, the holding table 21A is moved from the inspection positionPI to the pre-alignment position PA while holding the inspectedworkpiece W. Further, the elevator 254 moves the workpiece W to itsoriginal height position (step S7). In parallel with this movement ofthe workpiece W, the control unit 5 reads the image data from the memory52, and determines the presence or absence of scratches, defects, etc.at the gear Wb on the basis of the read workpiece images. In this way,workpiece inspection is conducted on the workpiece W held by the holdingtable 21A (step S8).

The workpiece W having returned to the pre-alignment position PA isgrasped by the unloader 42. Thereafter, the workpiece W is released fromthe grasp by the movable members 221 to 223. Thus, the transfer of theworkpiece W from the holding table 21A to the unloader 42 is carriedout. Next, the unloader 42 carries the workpiece W to the unloading unit4 and houses the workpiece W into the workpiece housing (not shown inthe drawings) (step S9). The foregoing sequence of steps (steps S1 toS9) is performed repeatedly and alternately by the holding tables 21Aand 21B.

Merely repeating the foregoing sequence of steps (steps S1 to S9)elongates cycle time for the presence of the pre-alignment process. Inthe embodiment, however, some of the steps on a workpiece W held by theholding table 21A and some of the steps on a workpiece W held by theholding table 21B are executed in parallel to encourage reduction incycle time. The following describes a technique of reducing cycle timein detail achieved by executing processes in parallel.

FIG. 6 is a flowchart showing operation performed in inspecting multipleworkpieces continuously, one by one, using the inspection apparatus inFIG. 1. In the embodiment, while the holding table 21A holding aworkpiece W is moved to the pre-alignment position PA and the inspectionposition PI and the holding table 21B holding a different workpiece W ismoved to the inspection position PI and the pre-alignment position PA,various steps are performed to inspect the workpieces W. In FIG. 6,regarding steps performed on the workpiece W held by the holding table21A and steps performed on the workpiece W held by the holding table21B, the latter steps are given dots visually to distinguish between theformer steps and the latter steps. Further, a flow of the stepsperformed on the workpiece W held by the holding table 21A is shown bysolid arrows meanwhile a flow of the steps performed on the workpiece Wheld by the holding table 21B is shown by dashed arrows. In an exemplarycase described below, of two continuous workpieces W, a previousworkpiece W is to be held by the holding table 21A and inspected, and anext workpiece W is to be held by the holding table 21B and inspected.

As described above, the previous workpiece W is carried by the loader 12of the loading unit 1 to the holding table 21A located at thepre-alignment position and grasped by the chuck mechanism 22 (step S1).Then, while the previous workpiece W is rotated and kept held by theholding table 21A, an image of the previous workpiece W is captured bythe alignment camera 27 (step S2). Image data resulting from thisimaging is stored into the memory 52. Next, the turning driver 262 makesa switch from the first position to the second position to move theprevious workpiece W and the holding table 21A together from thepre-alignment position PA to the inspection position PI (step S3).During this movement, misalignment is detected on the basis of the imagedata about the previous workpiece W (step S4). Then, the misalignment iscorrected at the holding table 21A (step S5). Meanwhile, as a result ofthe foregoing position switch, the holding table 21B is moved from theinspection position PI to the pre-alignment position PA. To narrow downa range of the description to the foregoing previous workpiece W and thenext workpiece W following the previous workpiece W, the descriptionwill be continued on the assumption that there is no workpiece W at theholding table 21B.

When the holding table 21A is located at the inspection position PI,images of the previous workpiece W held by the holding table 21A arecaptured by the inspection cameras 31 while the previous workpiece W isrotated in the aligned state. Data about these images is stored into thememory 52 (step S6). Meanwhile, the holding table 21B is located at thepre-alignment position PA. During the foregoing imaging of the previousworkpiece W, the next workpiece W is carried by the loader 12 of theloading unit 1 to the holding table 21B and grasped by the chuckmechanism 22 (step S1). Then, while the next workpiece W is rotated andkept held by the holding table 21B, an image of the next workpiece W iscaptured by the alignment camera 27. Data about this image is storedinto the memory 52 (step S2). In this way, in the embodiment, imaging ofthe previous workpiece W for inspection (step S6) is executed inparallel with loading of the next workpiece W (step S1) and imaging ofthe next workpiece W for detection of the misalignment (step S2).

After both these imaging processes are finished, the turning driver 262makes a switch from the second position to the first position to movethe previous workpiece W and the holding table 21A together from theinspection position PI to the pre-alignment position PA (step S7).During this movement, the image data about the previous workpiece W isread from the memory 52, and the previous workpiece W is inspected onthe basis of the read image data (step S8). Meanwhile, the nextworkpiece W and the holding table 21B are moved together from thepre-alignment position PA to the inspection position PI (step S3).During this movement, misalignment is detected on the basis of the imagedata about the next workpiece W (step S4). Then, the misalignment iscorrected at the holding table 21B (step S5).

When the holding table 21B is located at the inspection position PI,images of the next workpiece W held by the holding table 21B arecaptured by the plurality of inspection cameras 31 while the nextworkpiece W is rotated in the aligned state. Data about these images isstored into the memory 52 (step S6). Meanwhile, the holding table 21A islocated at the pre-alignment position PA. During the foregoing imagingof the next workpiece W, the previous workpiece W is carried from theholding table 21A to the unloading unit 4 by the unloader 42 of theunloading unit 4. By doing so, the holding table 21A becomes empty.Processes are repeated in the same way as the foregoing to inspect theplurality of workpieces W one by one in succession.

As described above, in the embodiment, on the basis of the image aboutthe workpiece W acquired by imaging of the workpiece W while theworkpiece W is rotated about the rotary axis AX3 by the holding table21A or 21B, displacement of the symmetry axis AX4 from the rotary axisAX3, namely, misalignment is detected. At each of the holding tables 21Aand 21B, the horizontal positioning mechanism 23 is provided to move thechuck mechanism 22 in a direction (in the embodiment, horizontaldirection) orthogonal to the rotary axis AX3 so as to eliminate theforegoing misalignment. In this way, the workpiece position iscorrected. This makes it possible to match the symmetry axis AX4 of theworkpiece W and the rotary axis AX3 of the motor 241 with each otherwith high accuracy and the workpiece W is subjected to inspection in theresultant aligned state, thereby achieving high-accuracy workpieceinspection.

In the embodiment, as shown in FIG. 6, the unloading step (step S9), theloading step (step S1), and the step of imaging of the uninspectedworkpiece W (step S2) are performed in parallel with imaging of thealigned workpiece W by the inspection camera 31 (step S6). Morespecifically, assuming that the aligned workpiece W is an “Nth (N≥2)workpiece W,” unloading of an (N−1)th workpiece W, loading of an (N+1)thworkpiece W, and imaging of the (N+1)th workpiece W by the alignmentcamera 27 proceed in parallel with imaging of the Nth workpiece W by theinspection camera 31. This makes it possible to reduce cycle timerequired for inspecting the plurality of workpieces W one by one insuccession.

In the embodiment, the position of a workpiece W is corrected bydetecting and correcting the misalignment in parallel with movement ofthe holding table 21A or 21B from the pre-alignment position PA to theinspection position PI. Further, the workpiece W is inspected on thebasis of an image captured by the inspection camera 31 in parallel withmovement of the holding table 21A or 21B from the inspection position PIto the pre-alignment position PA. These contribute to reduce tact timefurther. Movement of the holding table 21A or 21B to the inspectionposition PI may be started after the misalignment is detected on thebasis of the image of the workpiece W captured by the alignment camera27, and the misalignment may be corrected during this movement. In thiscase, comparable action and effect are achieved. More specifically,reduction in tact time can be encouraged by detecting the misalignmentand correcting the misalignment (correcting the position of theworkpiece W) at least partially in parallel with movement of the holdingtable 21A or 21B from the pre-alignment position PA to the inspectionposition PI.

The step of imaging of an uninspected workpiece W (step S2) of theembodiment corresponds to an example of a “first step” of the presentinvention. The step of moving the holding table 21A or 21B to theinspection position PI (step S3) of the embodiment corresponds to anexample of a “second step” of the present invention. The step ofdetecting misalignment (step S4) of the embodiment corresponds to anexample of a “third step” of the present invention. The step ofcorrecting the misalignment (step S5) of the embodiment corresponds toan example of a “fourth step” of the present invention. The step ofimaging of the aligned workpiece W (step S6) of the embodimentcorresponds to an example of a “fifth step” of the present invention.The step of inspecting the workpiece W (step S8) of the embodimentcorresponds to an example of a “sixth step” of the present invention.The step of moving the holding table 21A or 21B to the pre-alignmentposition PA (step S7) of the embodiment corresponds to an example of a“seventh step” of the present invention. The alignment camera 27 and theinspection camera 31 correspond to an example of an “alignment imagingpart” and an example of an “inspection imaging part” respectively of thepresent invention. The control unit 5 functions as a “workpiece positioncorrection part” and a “workpiece inspection part” of the presentinvention.

The present invention is not limited to the foregoing embodiment but canbe changed in various ways other than those described above within arange not deviating from the substance of the invention. For example, inthe foregoing embodiment, the present invention is applied to theworkpiece holder that holds a workpiece W with the gear Wb and theinspection apparatus equipped with the workpiece holder. However, thisis not the only type of workpiece W but the “workpiece” mentioned in thepresent invention covers every kind of workpiece having an outerperipheral portion rotationally symmetric about a symmetry axis.

The configuration of the foregoing embodiment is such that a workpiece Wis grasped by the three movable members 221 to 223. In an alternativeconfiguration, the workpiece W may be held by two, or four or moremovable members.

In the foregoing embodiment, the turning driver 262 causes the supportplate 261 to make turning motion to switch the positions of the holdingtables 21A and 21B. However, this is not the only position switchingmechanism. While the present invention is applied to the inspectionapparatus 100 that inspects workpieces W continuously while moving theworkpieces W from the pre-alignment position PA, to the inspectionposition PI, and then to the pre-alignment position PA by switching thepositions of the holding tables 21A and 21B using the holding tables 21Aand 21B, the present invention is further applicable to an inspectionapparatus that inspects workpieces W continuously while switching thepositions of three or more holding tables.

Although the invention has been described by way of the specificembodiments above, this description is not intended to be interpreted ina limited sense. By referring to the description of the invention,various modifications of the disclosed embodiments will become apparentto a person skilled in this art similarly to other embodiments of theinvention. Hence, appended claims are thought to include thesemodifications and embodiments without departing from the true scope ofthe invention.

INDUSTRIAL APPLICABILITY

The present invention is applicable to an inspection method and aninspection apparatus in general for inspecting a workpiece having anouter peripheral portion rotationally symmetric about a symmetry axis.

REFERENCE SIGNS LIST

-   -   5 control unit (workpiece position correction part, workpiece        inspection part)    -   21A holding table    -   21B holding table    -   27 alignment camera (alignment imaging part)    -   31 inspection camera (inspection imaging part)    -   100 inspection apparatus    -   AX3 rotary axis    -   PA pre-alignment position    -   PI inspection position    -   W workpiece

The invention claimed is:
 1. An inspection method of inspecting a plurality of workpieces one by one in succession, each of the workpieces having an outer peripheral portion rotationally symmetric about a symmetry axis, the method comprising: a first step of capturing an image of a first workpiece while holding the first workpiece at a pre-alignment position using a first holding table and rotating the first workpiece about a rotary axis; a second step of moving the first holding table holding the first workpiece to an inspection position different from the pre-alignment position after the first step; a third step of detecting misalignment of the symmetry axis of the first workpiece with respect to the rotary axis on the basis of the image of the first workpiece captured in the first step; a fourth step of correcting a position of the first workpiece at the first holding table so as to eliminate the misalignment detected in the third step; a fifth step of capturing an image of the first workpiece that have undergone a position correction while rotating the first workpiece about the rotary axis at the inspection position; a sixth step of inspecting the first workpiece on the basis of the image captured in the fifth step; and a seventh step of capturing an image of a second workpiece that is inspected while holding the second workpiece at the pre-alignment position using a second holding table and rotating the second workpiece about a rotary axis, wherein at least a part of the seventh step is executed while the fifth step is being performed.
 2. The inspection method according to claim 1, wherein the fourth step is performed in parallel with the second step.
 3. The inspection method according to claim 2, wherein the third step is performed in parallel with the second step.
 4. The inspection method according to claim 1, wherein further comprising: a an eighth step of moving the first holding table holding the first workpiece from the inspection position after implementation of the fifth step; and a ninth step of moving the second holding table holding the second workpiece to the inspection position after the seventh step, wherein the eighth step and the ninth step are performed simultaneously.
 5. The inspection method according to claim 4, wherein the sixth step is performed in parallel with the seventh step.
 6. An inspection apparatus comprising: a first holding table and a second holding table each of which is configured to hold a workpiece having an outer peripheral portion rotationally symmetric about a symmetry axis and rotates the workpiece about a rotary axis; an alignment imaging part that captures an image of a first workpiece held by the first holding table at a pre-alignment position; an inspection imaging part that captures an image of the first workpiece held by the first holding table at an inspection position different from the pre-alignment position; a workpiece position correction part that corrects the position of the workpiece, a symmetry axis of which is misaligned with the rotary axis of the first holding table, on the basis of an image acquired by imaging of the workpiece using the alignment imaging part while the workpiece is rotated about the rotary axis; and a workpiece inspection part configured to inspect the first workpiece that have undergone a position correction on the basis of an image acquired by imaging of the first workpiece using the inspection imaging part while the first workpiece is rotated about the rotary axis, wherein when the first holding tables is located at the pre-alignment position, the second holding tables is located at the inspection position, and at least a part of a process of imaging of the first workpiece is executed by the alignment imaging part while at least a part of a process of imaging of the second workpiece held by the second holding table is executed by the inspection imaging part. 